Centralizing and well-calipering apparatus for well tools

ABSTRACT

THE PARTICULAR EMBODIMENTS DISCLOSED HEREIN AS REPRESENTATIVE OF THE PRESENT INVENTION ARE DIRECTED TO NEW AND IMPROVED APPARATUS FOR CENTRALIZING WELL TOOLS AND FOR MEASURING THE DIAMETERS OF WELL BORES. IN PARTICULAR, THE DISCLOSED EMBODIMENTS EACH EMPLOY A PLURALITY OF OUTWARDLY-BOWED UPRIGHT SPRINGS SPACED CIRCUMFERENTIALLY AROUND A BODY AND ADAPTED TO CONTACT THE WALL SURFACES OF A WELL BORE AND CORRESPONDINGLY FLEX LATERALLY INWARDLY AND OUTWARDLY IN UNISON AS THE APPARATUS ENCOUNTERS DIAMETRICAL CHANGES IN A WELL BORE FOR MAINTAINING THE TOOL CONCENTRICALLY POSITIONED THEREIN. INDEPENDENT INWARD FLEXURAL MOVEMENTS OF LESS THAN ALL OF THE BOWED SPRINGS ARE PREVENTED, HOWEVER, BY MOVEMENT-RESPONSIVE MEANS UNIQUELY ADAPTED TO EQUILATERALLY POSITION THE WALLENGAGING PORTIONS OF THE BOWED SPRINGS FOR ACCURATELY   CENTRALIZING THE TOOL BODY IN A WELL BORE. IN AN ALTERNATIVE EMBODIMENT OF THE INVENTION, MEANS ARE FURTHER PROVIDED TO PRODUCE SIGNALS REPRESENTATIVE OF THE FLEXURAL MOVEMENTS OF THE BOWED SPRINGS FOR DERIVING DIAMETRICAL MEASUREMENTS OF A WELL BORE.

Jan. 19 1971 I w QUBBERLY, JR 3,555,689

CENTRALIZING AND WELL-CALIPERING APPARATUS FOR WELL TOOLS Filed Dec. 19, 1968 5 Sheets-Sheet 1 Walter E. Cubber/y, Jr

- INVENTOR.

ATTORNEY Jan. 19, 1971 w, E. CUBBERLY, JR 3,555,689

CENTRALIZING AND WELL-CALIPERING APPARATUS FOR WELL TOOLS Filed Dec. 19, 1968 3 Sheets-Sheet 2 FIG. 3A & FIG. 3B

Walter E. Cubberly, Jr

INVEN TOR FIG. 5

ATTORNEY Jan. 19, 1971 w. E. CUBBERLY, JR 3,555,689

CENTRALIZING AND WELL'-CALIPERING APPARATUS FOR WELL TOOLS 3 Sheets-Sheet 5 Filed D90. 19, 1968 Walter E Cubber/y, J17

INVENTOR A T TORNE V United States Patent 3,555,689 CENTRALIZING AND WELL-CALIPERING APPARATUS FOR WELL TOOLS Walter E. Cubberly, Jr., Houston, Tex., assignor to Schlumberger Technology Corporation, New York, N.Y., a corporation of Texas Filed Dec. 19, 1968, Ser. No. 785,154 Int. Cl. E21b 47/08 U.S. Cl. 33-178 12 Claims ABSTRACT OF THE DISCLOSURE The particular embodiments disclosed herein as representative of the present invention are directed to new andimproved apparatus for centralizing well tools and for measuring the diameters of well bores. In particular, the disclosed embodiments each employ a plurality of outwardly-bowed upright springs spaced circumferentially around a body and adapted to contact the wall surfaces of a well bore and correspondingly flex laterally inwardly and outwardly in unison as the apparatus encounters diametrical changes in a well bore for maintaining the tool concentrically positioned therein. Independent inward flexural movements of less than all of the bowed springs are prevented, however, by movement-responsive means uniquely adapted to equilaterally position the wallengaging portions of the bowed springs for accurately centralizing the tool body in a well bore. In an alternative embodiment of the invention, means are further provided to produce signals representative of the fiexural movements of the bowed springs for deriving diametrical measurements of a well bore.

It is, of course, quite common to move a so-called calipering tool through a well bore to obtain a record of its actual diameter at selected intervals. Typical of such tools are those shown in Pat. No. 2,639,512, Pat. No. 2,712,697 and Pat. No. 3,097,433 which respectively employ a plurality of outwardly-bowed wall-engaging springs having their ends slidably coupled to an elongated tool body by appropriate couplings. In this manner, as one of these calipering tools enters constricted sections of a well bore and the intermediate wall-engaging portions of the bowed springs are correspondingly deflected inwardly, the end-coupling members will be longitudinally separated a distance proportionally related to that particular diameter. Similarly, upon encountering an enlarged interval, the springs will flex outwardly and reposition the end-coupling members to a new longitudinal separation representative of the increased diameter. Thus, as the tool is traversed along a typical well bore, these variations in longitudinal spacing between the end-coupling members are successively translated by one or more suitable electromechanical devices on the tool into a meaningful record of well bore diameters as a function of well bore depth.

Although the calipering tools described in the abovementioned patents have been quite successful in substantially-vertical well bores, such tools are usually not well suited for service in those well bores having substantially deviated or inclined intervals. For example, as noted in the above-mentioned Cubberly Pat. No. 3,097,433, the forces maintaining the bowed springs against the Well bore walls must be relatively minimal to insure sensitivity as well as to not unduly impede movement of the calipering tool through the well bore. It will be appreciated, of course, that when even the Cubberly calipering tool is used in a greatly-inclined well bore, a significant portion of its net weight must be carried by those springs engaging the lower wall surfaces; and, in view of these above-men- 3,555,689 Patented Jan. 19, 1971 ICC tioned minimal forces, the net weight of the tool can become so great that the springs will collapse inwardly against the tool body. As a result, it has not been possible heretofore to use such tools for accurately measuring the diameters of those well bore intervals that deviate more than about 10 to 20 from the vertical.

Similar problems are also encountered in simply maintaining various types of well-logging tools accurately centered in even slightly-deviated well bores. For example, acoustic-logging tools such as that shown in. a copending application Ser. No. 765,892 filed Oct. 8, 1968, have recently been introduced to the oil industry for providing visual displays at the surface that are indicative of the character or surface condition of the surrounding well bore wall. Those skilled in this art will, of course, appreciate that the quality of their logging records will be significantly influenced by how accurately such tools (as well as other similar or wholly-different types of acoustic-logging tools) are centralized as they traverse a well bore.

Accordingly, it is an object of the present invention to provide new and improved apparatus for accurately centralizing well tools within even greatly-deviated well bores. It is a further object of the present invention to provide new and improved well-calipering apparatus.

These and other objects of the present invention are attained by arranging on a tool body a plurality of circumferentially-spaced, outwardly-bowed spring members adapted for cooperative flexural movements corresponding to various transverse spacings between the walls of a well bore contacted by outwardly-facing surfaces on the spring members. To maintain the tool body accurately centralized in a well bore, means are provided to prevent independent inward deflection of less than all of the springs for maintaining the wall-engaging surfaces of all springs equidistant from the tool axis at all times. Where apparatus of the present invention is to be used as a wellcalipering tool, measuring means are further included for providing a signal representative of the transverse spacings of the wall-engaging surfaces.

The novel features of the present invention are set forth with particularity in the appended claims. The invention, together with further objects and advantages thereof, may be best understood by way of the following descriptions of exemplary apparatus employing the principles of the invention as illustrated in the accompanying drawings, in which:

FIG. 1 shows a well-logging tool incorporating preferred embodiments of the present invention as this tool might appear while traversing a typical inclined borehole;

FIG. 2 is an enlarged isometric view of one of the centralizers shown in FIG. 1;

FIGS. 3A and 3B are schematic representations of an alternative embodiment of the present invention in different operating positions to illustrate the cooperative relation of various tool-centralizing elements thereof as well as to illustrate the utility of the present invention for obtaining diametrical measurements of well bores;

FIGS. 4A and 4B are cross-sectioned elevational views of the more-significant portions of an accurately-centraL ized well-calipering tool arranged in accordance with the present invention; and

FIG. 5 is a cross-sectional view taken along the lines 5--5 in FIG. 4A.

To illustrate one manner in which the invention may be effectively utilized, a well-logging tool 10 having upper and lower centralizers 11 and 12 in accordance with the present invention is depicted in FIG. 1 within a typical well bore such as a greatly-inclined borehole 13. As is typical, the upper end of the logging tool 10 is connected to the surface by a suitable suspension cable 14 having one or more electrical conductors. The logging tool is housed in a tubular body 15 having longitudinally-spaced portions thereof arranged to carry the centralizers 11 and 12 of the present invention. A resilient nose piece 16 is preferably mounted on the lower end of the body 15 to absorb shocks as well as to facilitate the descent of the tool through the borehole 13. The upper portion of the body is appropriately connected to the cable 14 by a typical cable head 17.

Although different types of logging tools can, of course, be employed with one or more of the centralizers of the present invention, the particular logging tool 10 shown in FIG. 1 is an acoustic-logging tool arranged as fully disclosed in the above-mentioned copending application for providing at the surface visual displays of the wall of the borehole 13. In general, the logging tool 10 includes repetitively-operable directional acoustic transducer means operating at a high frequency and adapted for rotation about the axis of the borehole 13. By progressively sweeping such repetitively-emitted high-frequency acoustic signals around the circumference of the borehole wall, corresponding reflected signals are obtained which will vary in accordance with various characteristics of the scanned borehole wall. Thus, as the logging tool 10 is traversed along the borehole 13, these reflected acoustic signals are appropriately converted to derive a record which is indicative of the characteristics of the successively-scanned portions of the borehole wall. Such records are, of course, particularly useful for indicating the presence of anomalies in the borehole wall as well as variations in the nature of the formation materials surrounding the borehole. In fact, the logging tool 10 is capable of producing visual displays having sufiicient resolution to portray even such minor anomalies as formation fractures in a borehole wall or perforations in a well casing. It will be appreciated, therefore, that to provide an accurate record, the logging tool 10 must at all times be maintained as close as possible to the center of the borehole 13. Since the particular details of the logging tool 10 are not related to the new and improved centralizers 11 and 12, however, no further description of this tool is required to understand the present invention.

Turning now to FIG. 2, an isometric view is shown of the tool-centralizing means 11 to illustrate a preferred embodiment of the present invention. In general, three pre-formed outwardly-bowed leaf springs 18a, 18b and 180 are disposed in upright positions and preferably spaced circumferentially around the body 15 at uniform intervals for lateral deflection (as shown by the arrows 19a and 1%) along respective radially-oriented planes of movement that converge with one another along the longitudinal axis 20 of the body. To operatively couple the spring members 18 to the body 15, the upper end of each spring is pivotally connected to a separate pivot 21 on an annular collar 22 that is loosely mounted on the body. In a similar fashion, the lower end of each bowed spring 18 is pivotally connected by an independent pivot 23 on another annular collar 24 loosely mounted on the body 15 well below the upper collar 22. It will be appreciated, therefore, that both of the centralizers 11 and 12 are free to shift longitudinally as well as rotate in relation to the tool body 15 and independently of one another.

Although the centralizer 11 is free to rotate as well as slide longitudinally in relation to the body 15, means are provided to limit the longitudinal shifting of the collars 22 and 24 toward one another without hindering their independent longitudinal movements along the body in response to the flexural movements 19 of the springs 18. To accomplish this, longitudinally-spaced abutments, as at 25 and 26, are respectively provided on the body 15 just below and above the collars 22 and 24 to prevent the collars from coming any nearer to one another than is required for the maximum laterally-outward extension of the springs 18. On the other hand, the tool body 15 is arranged so that any enlargements thereon (as at 27 and 28) are sufliciently spaced above and below the sliding 4 collars 22 and 24, respectively, as to not prevent free movement of either of the collars to a position where the bowed springs 18 will be fully collapsed or retracted against the body.

By arranging the longitudinal spacing between the abutment 25 and the enlargement 27 (as well as between the abutment 26 and the enlargement 28) in this manner, the upper collar 22 (and conversely the lower collar 24) is free to shift longitudinally the full distance required to accommodate the entire lateral deflection of the bowed springs 18 between their fully-extended positions and their fully-retracted positions. Accordingly, upon downward travel of the tool 10 through the borehole 13, the frictional contact of the bowed springs 18 with the borehole wall will shift the centralizer 11 upwardly in relation to the body 14 until the lower collar 24 is halted by the lower abutment 26. Once the lower collar 24 is halted, the flexural movements of the bowed springs 18 in accordance with diametrical variations in the borehole 13 will correspondingly shift only the upper collar 22 in relation to the tool body 15 within its respective span of travel between the upper abutment 25 and the body enlargement 27. Conversely, upon upward movement of the tool 10 in the borehole 13, the upper collar 22 will be shouldered against the upper abutment 25 and the flexural lateral movements of the bowed springs 18 will provide corresponding upward and downward shifts of the lower collar 24 between the lower abutment 26 and the body enlargement 28.

To urge the bowed springs 18 outwardly, biasing means are provided such as one or more tension springs 29 that are respectively arranged around the body 15 and operatively inter-connected between the upper and lower collars 22 and 24. It will be recognized, therefore, that the centralizing forces that are effective for maintaining the tool 10 centered in the borehole 13 are cooperatively supplied by the bowed springs 18 as well as the tension springs 29.

Accordingly, to achieve the most-efiicient centralizing effect for the tool 10, the bowed springs 18 and the tension springs 29 are cooperatively arranged in accordance with the teachings of Pat. No. 3,097,433 to provide substantially-constant and equal outwardly-acting centralizing forces over a wide range of well bore diameters. Inasmuch as the underlying theory and the design criteria for uniquely accomplishing this function are fully explained in that patent, the pertinent portions of that disclosure are simply incorporated herein by reference to avoid undue repetition.

It will be recognized, of course, that whenever the well tool 10 enters a deviated well bore interval such as the borehole 13, the centralizers 11 and 12 will inherently assume an angular orientation in relation to the tool body 14 so that two of the bowed springs 18 of each centralizer are riding along the lower surface of the borehole wall and the third bowed spring is in a generally-upright position and contacting the center of the upper surface of the borehole wall. As a result, therefore, the two lower springs 18 of each of the centralizers 11 and 12 must support the tool 10 (i.e., then net difference between the downwardly-acting component of the weight of the tool and any upwardly-acting buoyancy forces thereon from the well bore fluids) to centralize the tool. The upwardlyoriented bowed springs 18 will, however, not be subjected to this downwardly-acting net load.

Accordingly, it has been found that without the present invention, the tool 10 would instead be slightly eccentered in a deviated well bore since this above-described unequal load distribution would slightly flatten the mid-portions of the two lower bowed springs 18 of each of the centralizers 11 and 12 and produce a corresponding bulge in the other upright bowed spring. Although this slight displacement from a truly-centralized position would be only negligible in nearly-vertical well bores, upon increase of either the deviation of a well bore or the net downward load on the lower of the bowed springs 18, the

degree of lateral displacement of the tool would, of course, become more significant. In either instance, with acoustic-logging tools as at 10, even slight lateral displacements from the true axis of a well bore will produce inferior visual displays.

Thus, in keeping with the objects of the present invention, means are provided for reliably maintaining the midportions of the bowed springs 18 of the centralizers 11 and 12 laterally equidistant from the axis 20 of the tool body 15 even when there is an unequal load imposed on only one or two of the bowed springs. To accomplish this, laterally-movable, longitudinally-oriented toggle linkages respectively comprised of upper and lower rigid arms, as at 30 and 31, are operatively arranged on each of the centralizers 11 and 12 for lateral movement in the aforementioned radially-oriented planes between each of the springs 18 and the tool body 15. As best seen in FIG. 2, the opposed ends of each pair of the rigid arms 30 and 31 for the centralizer 11 are pivotally interconnected, as at 32, and respectively positioned immediately behind the mid-portion of their associated bowed spring 18. The other ends of each pair of the rigid arms 30 and 31 are respectively pivotally coupled, as at 33 and 34, to the upper and lower collars 22 and 24 for pivoting the arms in these aforementioned radially-oriented longitudinal planes of movement including the tool axis 20. It will be appreciated, therefore, that the interconnected ends 32 of each pair of the rigid arms 30 and 31 are laterally movable in relation to the tool body 15 in the same radial plane of flexural movement of their respectively-associated bowed spring 18. In other words, longitudinal movement of the sliding collars 22 and 24 is effective to jointly move each pair of the rigid arms 30 and 31 in a selected longitudinal plane respectively defined by the tool axis 20 and the particular plane of deflection of the associated bowed spring 18.

Accordingly, it will be appreciated that at any given relative longitudinal position of the sliding collars 22 and 24, the mid-portions of the bowed springs 18 cannot move any closer to the body 15 than permitted b the pivotallyinterconnected ends 32 of the rigid arms 30 and 31. Moreover, since each pair of the arms 30 and 31 are identically arranged, these pivotally-interconnected ends 32 will always be equidistant from the tool axis 20 and thereby prevent unequal inward deflectional movements of the bowed springs 18.

It will be appricated, therefore, that as the sliding collars 22 and 24 are shifted back and forth along the tool body 15 in accordance with diametrical variations in the borehole 13, the interconnected ends 32 of the rigid arms 30 and 31 will also be selectively moved in unison to their respective corresponding equidistant lateral position along with the bowed springs 18. Thus, in any given longitudinal position of the collars 22 and 24 in relation to one another, the interconnected linkage ends 32 will simply prevent further inward deflection or lateral flexural movements of the mid-portions of less than all of the bowed springs 18 such as, for example, might be caused by the above-discussed flattening of those bowed springs 18 that are supporting the net weight of the tool 10. It should be noted in passing that measures must be taken to prevent the interconnected ends 32 from coming so close to the body 15 that each pair of the rigid arms 30 and 31 are in coincidental alignment with one another and, as a result, might not be capable of re-extension. Appropriatelylocated stops (not shown) can, however, be provided to always insure that the rigid arms 30 and 31 are at a slight angle when the bowed springs 18 are fully retracted.

On the other hand, any diametrical variations in the borehole 13 encountered by the centralizer 11 (or 12) will immediately be eifective to reposition the springs 18 as required to maintain the tool body 15 in accurate coaxial alignment within that interval of the borehole. Thus, whenever the tool 10 encounters a reduced-diameter portion of a well bore, for instance, once the movement of the tool therein imposes a suflicient load on the bowed springs 18 to exceed the design contralizing force and accordingly compresses the springs, the trailing collar (either 22 or 24) will be shifted to a new longitudinal position along the tool body 15 further separated from the leading collar. This change in the relative longitudinal spacing of the sliding collars 22 and 24 will, of course, be effective to simultaneously retract the bowed springs 18 and rigid arms 30 and 31 so as to relocate the interconnecting arm ends 32 in unison to new corresponding equilateral positions immediately behind the rear faces of the mid-portions of the bowed springs. Similarly, whenever the centralizer 11 (or 12) moves into an enlarged well bore interval, the cooperative interaction of the springs 18 and 29 will correspondingly reposition the trailing collar (22 or 24) in relation to the other collar so as to simultaneously extend the bowed springs and rigid arms 30 and 31, with the interconnected link ends 32 again moving in unison to assume new equidistant lateral positions immediately adjacent to the rear of the wall-engaging surfaces of the bowed springs.

Accordingly, it will be appreciated that the interconnected arm ends 32 are operatively positioned in unison at all times at equilateral positions corresponding to the equilateral positions that the mid-portions of the bowed springs 18 should assume if there were no unbalanced forces acting thereon. Thus, by equilaterally positioning the interconnected arm ends 32, unbalanced forces acting on the bowed springs 18 will be ineffective to eccenter the tool body 15 until the design centralizing force is exceeded. Once this happens, however, the cooperative arrangement of the centralizers 11 and 12 of the present invention will quickly reposition the tool body 15 to the equilateral center of that interval of the well bore.

The length of the rigid arms 30 and 31 as well as the locations of the pivots 33 and 34 must, of course, be coordinated so as to always maintain the interconnected linkage ends 32 immediately adjacent to the mid-portions of the bowed springs 18 as they move inwardly and outwardly, these parameters can, however, be readily determined by diagraming the path followed by the mid-portion of one of the bowed springs 18 between its maximum and minimum lateral positions. As previously mentioned, as the logging tool 10 moves through a well bore, the leading or advance collar (22 or 24) will be engaged against its associated abutment (25 or 26) and only the trailing collar (24 or 22) will be free to shift longitudinally in relation 3 to the tool body 15. Accordingly, the mid-portion of the diagramed spring 18 will follow an arcuate path that progressively moves further away from the stationary leading collar (22 or 24) as the bowed spring is collapsed. This arcuate path is substantially circular in nature so that a fixed center can be diagrammatically determined on the stationary leading collar for accurately finding the necessary location of the pivots 33 and 34 as well as the length of the arms 30 and 31 required for the interconnected arm ends 32 to closely follow this arcuate path. Since the upper and lower portions of the bowed springs 18 are symmetrical, it will be appreciated, of course, that the arms 30 and 31 will be equal in length.

Expansion and contraction of the bowed springs as a tool carrying them moves through a well bore will, of course, cause correspondin predictable longitudinal movements of the ends of the bowed springs in relation to one another. Assuming, for example, that (as shown in FIG. 3A) a well tool 50 having a centralizer 51 arranged in accordance with the invention is moving downwardly through an enlarged interval of a well bore 52, the frictional drag of the bowed springs 53 thereon will shift the centralizer upwardly along the tool body 54 until the lower sliding collar 55 hereof engages a body stop 56. The upper collar 57 of the centralizer 51 will then be free to move between spaced body stops 58 and 59. Thus, as the tool 50 continues to move downwardly, diametrical variations in the well bore 52 will cause the bowed springs 53 7 to deflect and correspondingly shift the sliding collar 57 longitudinally along the tool body 54 in proportion to the lateral deflections of the bowed springs.

It will also be appreciated that, as shown in FIG. 3B, the reverse action will be obtained upon upward movement of the tool 50 in the well bore 52. In this instance, the upward travel of the tool 54} will cause the centralizer 51 to shift downwardly in relation to the tool body 54 until the upper collar 57 is abutted on the body stop 58 and it will now be the lower collar 55 that will independently shift longitudinally in relation to the body stop 56 in proportion to the deflections of the bowed springs 53.

Accordingly, irrespective of the direction of travel of the tool 50 in a well bore, lateral deflections of the bowed springs 53 will produce corresponding shifts of one or the other of the collars 55 and 57 that are proportionally related to the transverse spacings of the wall-contacting surfaces of the bowed springs. In one manner of translating these independent longitudinal movements of the collars 55 and 57 into meaningful information, electrical control means, such as a potentiometer 60, having an electrical characteristic that will be predictably varied in response to a specified movement are operatively coupled to the collars. For example, as seen in FIGS. 3A and 3B, by operatively coupling the resistance element 61 of the potentiometer 60 to the upper collar 57 and the sliding contact 62 of the potentiometer to the lower collar 55, flexural movements of the bowed springs 53 will correspondingly vary the relative positions of the sliding contact and the resistance element. Thus, by means of appropriate electrical circuitry (not shown), these changes in the relative positions of the potentiometer 60 can readily be translated into meaningful electrical indications from which the radial spacings of the wall-contacting surfaces of the bowed springs 53 can be determined to continuously measure an average diameter of the Well bore 52.

Turning now to FIGS. 4A and 4B, successive crosssectional views in elevation are shown of the more significant portions of a preferred embodiment of the wellcalipering tool 50. As seen there, the tool body 54 is tubular and the various elements of the tool 50 already described are identified with their respective reference numerals. Inasmuch as the functional relations of these previously-described elements have already been brought out, it is believed necessary only to now point out various significant constructional features of the tool 50-. Moreover, to clarify the description of the constructional features, various minor features such as joint details have either been omitted or are simplified in some respects. Similarly, only one of the bowed springs 53 have been shown to simplify the drawings.

Accordingly, as seen in FIG. 4A, the upper portion of the tool body 54 is preferably arranged to isolate the potentiometer 60 from well bore fluids and the like by enclosing it in an oil-filled chamber, as at 63, and fluidly sealing around electrical conductors and other elements leaving the chamber. This, of course, makes it necessary to pressure-balance the chamber 63 as well as to arrange the potentiometer 60 for independent movement therein. To accomplish this, the potentiometer 60 is preferably of a type having a tubular body 64 carrying a helicallywound resistance element (as at 61) and an axially-movable control rod 65 carrying the sliding contact (as at 62). An upright extension 66 of the potentiometer body 64 is slidably disposed in an appropriately-located opening in a transverse guide '67 across the enclosure 63.

Although the control rod 65 could possibly be passed through fluid seals and directly connected to its associated sliding collar 55, it is preferred to maintain this typically-slender control rod in tension to prevent its buckling. To accomplish this, a depending tubular extension 68 is connected to the lower end of the tubular potentiometer body 64 and slidably passed through an annular seal 69 in a complementary opening in a transverse wall 70 extending across the upper portion of the tool body 54.

An extension shaft 71 is suitably connected, as at 72, to the lower end of the control rod 65 and extended downwardly through the tubular body extension 68 and slidably passed through an annular seal 73 carried on a closure plug 74 secured to the lower end of the body extension. A compression spring 75 is coaxially arranged in the body extension 68 and compressed between a shoulder (as at 76) on the shaft coupling 72 and the end closure 74. It will be appreciated, therefore, that the seals 69 and 73 as well as the transverse wall 70 and the body extension 68 cooperatively define the lower walls of the oil chamber 63. Moreover, by virtue of the seal 69, the potentiometer body 64 is free to move longitudinally in relation to the oil chamber 63 and the tool body 54; and, by virtue of the seal 73, the potentiometer control rod 65 is also free to move longitudinally relative to both the oil chamber and tool body. Thus, longitudinal movement in either direction of the potentiometer body 64 (and the resistance element 61) is accomplished by moving the closure plug 74. Similarly, downward longitudinal movement of the shaft extension 71 will correspondingly move the sliding contact 62, with upward movement of the sliding contact being provided by expansion of the compression spring 75 when the shaft exten sion is moved upwardly thereby.

According, to employ the longitudinal movements of the sliding collars 55 and 57 for controlling the potentiometer 60, as seen in FIGS. 4A and 4B, the potentiometer body extension 68 is connected to the upper sliding collar 57 and the potentiometer shaft extension 71 is con nected to the lower sliding collar 55 to obtain the desired independent movements of the resistance element 61 and the sliding contact 62. As best seen in FIGS. 4A and 5, the upper sliding collar 57 is slidably mounted on the tool body 54 above the body stop 58 and pivotally connected to the upper ends of the bowed springs 53. Since the upper collar 57 must be capable of rotating freely in relation to the tool body 54, an annular recess 77 is formed in the upper end of the collar to loosely receive a ring 78. To connect the ring 78 to the potentiometer bdy 64, the ends of the a transverse pin 79 are passed through longitudinal slots 80 and 81 on opposite sides of the tool body 54 and coupled to the ring, with the central portion of this pin being confined within an adjacent portion of a circumferential groove 82 formed around the end closure plug 74. Thus, irrespective of the angular position of the collar 57 as determined by the angular position of the centralizer 51, the ring 78 and transverse pin 79 carried thereby will readily follow longitudinal movements of the sliding collar and transfer these movements through the body extension 68 to the resistance element 61 of the potentiometer 60.

To control the sliding contact 62 of the potentiometer 60, the free end of the potentiometer shaft extension 71 is connected as seen in FIGS. 4A and 4B to the upper end of a flexible cable 83 by a clevis 84, with the lower end of the cable being connected by another clevis 85 to a body 86 carrying a transverse pin 87. The free ends of this transverse pin 87 are respectively passed through longitudinal slots, as at 88, on opposite sides of the tool body 54 and connected to a ring 89 slidably mounted on the exterior of the tool body. The sliding collar 55 carrying the lower ends of the bowed springs 53 is formed with an inwardly-facing annular groove 90 for loosely confining the sliding ring 89. Thus, even though the collars 55 and 57 are free to rotate as well as to slide in relation to the tool body 54, their respective sliding rings 78 and 89 are free to only slide longitudinally for respectively positioning the resistance element 61 and sliding contact 62 of the potentiometer 60 in accordance with the relative longitudinal positions of the sliding collars as the bowed springs 53 flex inwardly and outwardly. It will be appreciated, therefore, that control of the potentiometer 60 is accomplished as the collars 55 and 57 are moved by the fiexural movements of the bowed springs 53. It will be further appreciated that the spring 75 will cooperably make up any longitudinal play in the series of linking connections between the potentiometer 60 and the collars 55 and -7.

Referring again to FIGS. 3A and 3B, it will be appreciated that the rigid arms 91 and 92 of the toggle linkage supporting the bowed springs 53 will provide a measure of accuracy not possible heretofore with well-calipering tools. By way of explanation, since the rigid arms 91 and 92 are pivotally interconnected, as at 93, and respectively pivoted to the collars 57 and 55, there is a precise trigonometric relationship between any given lateral spacing of the interconnected arm ends 93 from the tool body 54 and the corresponding longitudinal spacing between the collars 5S and 57. Thus, the calibration of an electrical device, such as the potentiometer 60, will be considerably more accurate than was possible heretofore. Moreover, with calipering tools such as that shown in the Cubberly patent, it was necessary to base the calibration of the measuring device on the characteristics of the several springs of the tool. In time, therefore, as these springs would wear or perhaps weaken, the calibration of the measuring device would be correspondingly impaired.

Accordingly, it will be recognized that the well-calipering tool 50 has a very accurate calibration which will not be afiected by either wearing of the springs 53 and 94 or changes in their respective characteristics. It will also be appreciated that since the calibration of the potentiometer 60 is independent of the characteristics of the springs 53 and 94, the strength of the tension springs can be temporarily increased if, for example, the calipering tool 50 is to be employed with a particularly heavy well tool. It will be recognized by inspection of FIG. 4 in the aforementioned Cubberly patent, stronger tension springs 94 will, of course, increase the net centralizing forces as well as cause the centralizing forces to increase as the well bore diameter increases. This, however, will not affect the accuracy of the calipering measurements and will allow the calipering tool 50 to be used either with heavier tools or in exceptionally deviated well bores so long as the combined tools can be moved downwardly therein.

Accordingly, although changes and modifications may be made in the disclosed embodiments without departing from the principles of the present invention as defined in the appended claims, it will be appreciated that the present invention provides new and improved means for accurately centralizing a well tool in a well bore. By arranging the linkage means in the unique manner shown for the disclosed embodiments, the wall-engaging members are accurately positioned at an appropriate equidistant position and reliably restrained to prevent inward movement of less than all of the members. Moreover, by virtue of the precise relationship between the positions of the several linkage elements, accurate calipering measurements can be readily secured by inclusion of suitable movement-responsive means.

What is claimed is:

1. A well tool adapted for passage through a well bore and comprising: a support; coupling means operatively mounted on said support for longitudinal movement between selected positions thereon; centralizing means including a plurality of independently-movable wallengaging members operatively arranged around said support and having first portions coupled to said coupling means and second portions spaced from said first portions 3. The well tool of claim 1 wherein said locating means include a plurality of rigid members respectively arranged between said support and each of said wall-engaging members, said rigid members having first end portions pivotally mounted on said coupling means and second end portions respectively disposed adjacent to said second portions of each of said wall-engaging members for preventing independent inward movements of said wall-engaging members without limiting independent outward movements of said wall-engaging members.

4. The well tool of claim 3 further including spring means adapted for urging said wall-engaging members outwardly with equal force.

5. A well tool adapted for passage through a well bore and comprising: a support; a plurality of arcuately-curved elongate spring members operatively arranged around said support, each of said arcuate spring members having upper and lower end portions longitudinally spaced along said support and an outwardly-bowed intermediate portion laterally spaced from said support; upper and lower coupling members longitudinally spaced on said support and respectively coupling said upper and lower end portions of said arcuate spring members to said support, at least one of said upper and lower coupling members being adapted for longitudinal movement along said support between a distant position from the other of said coupling members for retracting said arcuate spring members adjacent to said support and other positions nearer to said other coupling member for extending said intermediate portions of said arcuate spring members outwardly into engagement with the wall surfaces of a well bore; means adapted for moving said one coupling member toward its said other positions to urge said intermediate portions of said arcuate spring members outwardly with equal force; and means on said support and responsive to movement of said one coupling member between its said positions for locating said intermediate portions of said arcuate spring members at equidistant positions from said support and preventing independent movements thereof from said equidistant positions to retain said support centrically disposed in a well bore.

6. The well tool of claim 5 further including means responsive to movements of said one coupling member between its said positions and adapted for providing signals at the surface representative of the lateral spacing between said support and said intermediate portion of at least one of said arcuate spring members. 7. The well tool of claim 5 wherein said locating means include a plurality of rigid arms respectively arranged behind each of said arcuate spring members and pivotally coupled to said one coupling member for movement thereby in unison as said one coupling member moves between its said positions to continuously support said intermediate portions of said arcuate spring members at their various said equidistant postions.

8. The well tool of claim 7 further including means responsive to movements of said one coupling member between its said positions and adapted for providing signals at the surface representative of the lateral spacing between said support and said intermediate portion of at least one of said arcuate spring members. 9. The well tool of claim 5 wherein said locating means include a plurality of toggle linkages respectively arranged behind each of said arcuate spring members, each of said toggle linkages including upper and lower rigid arms re spectively pivoted from said upper and lower coupling members and pivotally interconnected at their opposed ends to provide a supporting surface adapted to engage the rear of said intermediate portion of their respectivelyassociated arcuate spring member; said toggle linkages being identical to one another so that, as said one coupling member moves between its said positions, said supportin surfaces will be correspondingly moved in unison to said equidistant positions and prevent independent inward movements of said arcuate spring members.

10. A Well tool adapted for passage through a well bore and comprising: a support; upper and lower coupling members operatively mounted on said support for longitudinal movements relative to one another between selected positions on said support; a trio of OUtWBIdIY bOWEd elongated leaf springs symmetrically arranged around said support with their upper and lower ends respectively coupled operatively to said upper and lower coupling members for correspondingly moving said coupling mem- Ibers between said selected positions in accordance with inward and outward flexural movements in unison of the intermediate bowed portions of said leaf springs; spring means urging said coupling members toward one another for deflecting said intermediate portions of said leaf springs outwardly toward the wall surfaces of a well bore; and equilaterally-positioned stop means behind each of said intermediate portions of said leaf springs and responsive -to longitudinal movements of said coupling members for preventing independent inward flexural movements of said leaf springs.

11. The well tool of claim 10 wherein said equilaterallypositioned stop means are comprised of three identical linkage means respectively disposed between each of said leaf springs and said support, each of said linkage means including an upper rigid arm pivotally coupled to said upper coupling member and having an end extended downwardly, a lower rigid arm pivotally coupled to said lower coupling member and having an end extended upwardly, and means pivotally interconnecting said extended ends of said rigid arms and defining a support adapted for engagement with the rear of its associated leaf spring and preventing inward deflection thereof unless said coupling members are moved apart in relation to one another.

12. The well tool of claim 11 further including electrical means operatively arranged between said coupling members for providing a distinctive electrical signal characteristic of the relative spacing between said coupling members.

References Cited UNITED STATES PATENTS 1,708,354 4/ 1929 CaJbot 33-178UX 1,893,600 1/1933 Shull 33205 1,898,074 2/1933 Bailey 166241 3,092,182 6/1963 Blagg 33178F SAMUEL S. MATTHEWS, Primary Examiner US. Cl. X.R. 166241 

